She carded three birdies and two bogeys and came agonisingly close to securing the outright lead on the 18th only for her birdie putt to go wide. She missed only one fairway and was solid in her approach play.
Ko will be expected to triumph today, which is something she's coming to grips with. It's just one thing she's coming to grips with but she's adamant life hasn't changed since becoming the youngest player - man or woman - to reach No1 in golf history.
"Not really," Ko said told the LPGA webstie. "I've only been No 1 the last two weeks so nothing's really changed. I try to keep to the same mindset playing in the Bahamas and I finished with a top 10 finish so that was really good. I just have to take every tournament and just concentrate on that because the rankings come afterwards."
Ko admitted there was "more media attention, more congratulations on social media" but on the course, everything is the same.
"I personally think this is the start," Ko said. "Golf is a sport that you can play for many years, and that's my plan. This is only the start of my second year on Tour. I've been enjoying that and I'm really looking forward to what's coming up next."
That' starts today with an Australian Open to win.
Elsewhere, Kiwi golfer Danny Lee has slipped to a share of 42nd at the Northern Trust Open on the PGA Tour after carding a two-over 73 during the second round in California. Lee made the cut despite tumbling 25 places down the leaderboard.
Compatriot Tim Wilkinson wasn't so fortunate, missing the cut by one stroke after shooting one-under to follow the three-over he managed in the first round.